The driverless vehicle of the present invention is of type disclosed in U.S. Pat. No. 3,356,040. The typical driverless vehicle of this type includes a deck having support wheels which ride on a pair of tracks. The vehicle is driven by the interrelationship between a drive wheel supported by the deck and a drive tube disposed between the tracks and in contact with the drive wheel.
The problem involved is as follows. When a vehicle is empty or has no load, it takes very little force to drive the vehicle. When the vehicle has a heay load, a large force is needed to move the vehicle. One solution was to attain an increased driving force by using two drive wheels coupled together on a common support. See U.S. Pat. No. 3,818,837 which teaches such plural drive wheels.
Another solution to the problem has been the use of a specially designed drive wheel with a large spring force thereby requiring a very heavy vehicle deck to hold the vehicle on the track when it is empty. If the deck is too light, the spring force lifts the vehicle off the track. The second alternative increases the cost of the vehicle and the system drive requirements.